Characteristics reactions of proteins.

October 13, 2014

Session 8 – Characteristics reactions of proteins.

 Aim

Students will identify the physical and chemical agents that cause the denaturation of proteins.

 Hypothesis

Coagulation and precipitation are characteristics of proteins,

 Materials

-Materials and equipment

✓ Test tube rack

✓ Test tubes

✓ Beaker

✓ Stirring rod

✓ Pipette

✓ Thermometer

✓ Suction cups

-Reactants and samples

 Egg white solution

 Ethylic alcohol

 Concentrated hydrochloric acid solution

 10% hydrochloric acid solution

 HNO3

 Concentrated sodium hydroxide solution

 1% copper sulfate solution

 Methods

A. Coagulation of albumin.

1. Add 2 mL of egg white solution to each of 5 test tubes.

2. Heat the first tube in a water bath and register the approximate temperature at which coagulation takes place.

3. Add 10 drops of ethylic alcohol to the second tube.

4. Add 6 drops of concentrated hydrochloric acid solution.

5. Add 15 drops of concentrated sodium hydroxide to the fifth tube.

6. Register the cases in which coagulation takes place and explain why it happened only in those cases.

B. Cation-based precipitation of a protein

Add to each of the test tubes the following:

1. 5 mL of water.

2. 5 mL of egg white solution.

3. 5 mL of water and 4 drops of 10% hydrochloric acid.

4. 5 mL of egg white solution and 4 drops of 10% hydrochloric acid.

5. 5 mL of water and 4 drops of 10% sodium hydroxide solution.

6. 5 mL of egg white solution and 4 drops of 10% sodium hydroxide solution.

Next, add 20 drops of 1% copper sulfate solution to each one of the 6 tubes and register the changes that occur. The blank tubes, those where no protein is added, are needed to determine if the effect of observed is really due to the precipitation of the protein or, rather, to the precipitation of a metallic hydroxide.

 Results

Coagulation

Test tube Observation Coagulation presence

T1

(Egg white + Heat) The egg protein coagulated at 64°C YES

T2

(egg white + ethylic alcohol) A jelly substance at the bottom and a pink liquid at the top were formed. YES

T3

(Egg white + concentrated hydrochloric acid) Small portions of a white substance were formed. NO

T4

(Egg white + concentrated nitric acid) It turned completely white. YES

T5

(Egg white + concentrated sodium hydroxide) It turned completely transparent and less dense. NO

Coagulation Results

Cation-based precipitation of a protein

Test tube Observation Precipitation presence

T1

(Water + cooper sulfate solution) No change. NO

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